Combination of extractive distillation and liquid extraction process for separation of a hydrocarbon feed mixture

ABSTRACT

An extractive distillation zone is used in combination with a liquid phase extraction zone to provide relatively highly aromatic heavy and light extracts and a relatively aromatic-free raffinate stream. The process allows a feed mixture which contains raffinate materials in at least two fractions of aromatics to contact an extractive distillation zone in which solvent passed thereinto dissolves the heavy aromatics from the feed stock. The overhead vapors from the extractive distillation zone are condensed and passed into a liquid phase extraction zone where the light aromatic fraction of the feed stock is extracted and substantially separated from the non-aromatic raffinate components. The raffinate, light extract and heavy extract materials are separately recovered. The process is applicable to most hydrocarbon separations and in particular can be used in the petrochemical industry to separate close boiling aromatic and non-aromatic materials.

Vickers et al.

[ 1 Oct. 29, 1974- COMBINATION OF EXTRACTIVE DISTILLATION AND LIQUIDEXTRACTION PROCESS FOR SEPARATION OF A HYDROCARBON FEED MIXTUREInventors: Anthony G. Vickers; Robert A.

Lengemann, both of 20 UOP Plaza Algonquin & Mt. Prospect Roads, DesPlaines, 111. 60016 Apr. 2, 1973 Appl. No.: 347,587

US. Cl 203/46, 203/58, 208/313, 208/325, 260/674 R, 260/674 A, 260/674SE Int. Cl. C07c 7/08, C070 7/10, BOld 3/40 Field of Search .Q203/43-46,

203/58, 84; 208/313, 325; 208/313, 325; 260/674 R, 674 A, 674 SEReferences Cited UNITED STATES PATENTS Thompson 203/58 6 x tract/yeStripper Primary Examiner-Wilbur L. Bascomb, Jr. Attorney, Agent, orFirmJames R. Hoatson, Jr.; Robert W. Erickson; William H. Page, II

[57] ABSTRACT An extractive distillation zone is used in combinationwith a liquid phase extraction zone to provide relatively highlyaromatic heavy and light extracts and a relatively aromatic-freeraffinate stream. The process allows a feed mixture which containsraffinate materials in at least two fractions of aromatics to contact anextractive distillation zone in which solvent passed thereinto dissolvesthe heavy aromatics from the feed stock. The overhead vapors from theextractive distillation zone are condensed and passed into a liquidphase extraction zone where the light aromatic fraction of the feedstock is extracted and substantially separated from the non-aromaticraftinate components. The raffinate, light extract and heavy extractmaterials are separately recovered. The process is applicable to mosthydrocarbon separations and in particular can be used in thepetrochemical industry to separate close boiling aromatic andnon-aromatic materials.

16 Claims, 1 Drawing'Figure Extract Column Exrracr Column COMBINATION OFEXTRACTIVE DISTILLATION AND LIQUID EXTRACTION PROCESS FOR SEPARATION OFA HYDROCARBON FEED MIXTURE BACKGROUND OF THE INVENTION 1. Field of theInvention The field of art to which this invention pertains is acombination extractive distillation-liquid phase extraction process.More particularly, this process is applicable to the extraction art andin particular to the hydrocarbon separation processes or petrochemicalseparation processes.

2. Description of the Prior Art The prior art related to solventextraction processes and combinations thereof has attempted to solve theproblems associated with the separation of nonaromatics from an aromaticcontaining feed stock which is to be separated into at least twoaromatic rich fractions. The old processes have typically utilized suchflow schemes as pre-fractionation of the feed stock to remove heavyaromatics from the feed stock followed by passage of the remainingnon-aromatics and light aromatics into a liquid phase extraction zonewhere the final separation of non-aromatics from the light aromatics canbe accomplished thereby rendering a heavy aromatic stream, a lightaromatic stream and a non aromatic raffinate stream. Some of the otherprior art processes have utilized a prefractionation zone to separate afeed stock into two boiling range materials with the overhead andbottoms fractions from the fractionator going to separate aromaticseparation systems. In this manner the feed stream is separated into twononaromatic raffinate fractions and two aromatic fractions.

The process of our invention allows a feed stock which contains a broadrange of aromatic boiling components and non-aromatic components to beseparated into a heavy aromatic stream, a light aromatic stream and araffinate stream through the use of combination of an extractivedistillation column and a liquid phase extraction zone and offerscertain advantages when compared to the use of dual liquid phaseextraction zones.

A dual liquid phase extraction combination requires a pre-fractionatorin addition to the two liquid phase extractors. The process of ourinvention can essentially eliminate the need for a pre-fractionator andthe use of a separate liquid phase extractor and provide a single zone(the extractive distillation zone) in which the combination of liquidphase extraction and prefractionation of the heaviest components of thefeed stock can be combined in a single operation.

SUMMARY OF THE INVENTION Our invention is a combination processutilizing an extractive distillation zone which allows a feed stock tobe separated into a heavy aromatic containing extract stream and anoverhead vapor stream. The overhead vapor stream is condensed and thenpassed into a liquid phase extractor for separation of the remainingnonaromatics from the remaining lighter aromatic components. Thenon-aromatic raffinate material from the liquid phase extractor can berecovered as can be the aromatics present in the light aromaticcontaining extract stream. This process combination allows recovery ofan aromatic free raffinate stream and non-aromatic free light and heavyextract streams.

A broad embodiment of our invention resides in a process for therecovery of two aromatic fractions and non-aromatics from a hydrocarbonfeed mixture containing aromatic and non-aromatic hydrocarbons, whichprocess comprises: (a) passing said feed into an extractive distillationzone maintained under extractive distillation conditions including thepresence of liquid solvent capable of selectively dissolving a firstaromatic fraction of said two fractions to provide a first rich solventstream containing said first aromatic fraction and a first overheadvapor stream comprising non-aromatic and second aromatic fractionmaterial; (b) recovering said first aromatic fraction from said firstrich solvent and passing solvent remaining after said recovery back tosaid extractive distillation zone of step (a); (c) condensing at least aportion of said first overhead vapor stream to form a condensed feed;(d) passing condensed feed into a liquid phase extraction zonemaintained at extraction conditions including the presence of a liquidsolvent capable of selectively dissolving the second aromatic fractionmaterial in said condensed feed and a hereinafter defined reflux toprovide a second rich solvent stream containing the second aromaticfraction and non-aromatics and a raffinate phase comprising non-aromatichydrocarbons; (e) passing said second rich solvent stream into astripping zone maintained under stripping conditions to removenonaromatics from said second rich solvent to provide a second overheadvapor comprising non-aromatics and a third rich solvent comprising saidsecond aromatic fraction and solvent; (f) condensing second overheadvapor and returning at least a portion thereof to said liquid-liquidextraction zone of step (d) as the above mentioned reflux; (g)recovering said second aromatic fraction from said third rich solventand passing solvent remaining after said recovery back to said liquidphase extraction zone.

BRIEF DESCRIPTION OF THE DRAWING The attached drawing illustrates apreferred embodiment of the process flow of our invention.

A feed stream which contains non-aromatic hydrocarbons together with atleast two different boiling range aromatic hydrocarbons passes via line14 into extractive distillation zone I. Extractive distillation zone 1is operated at extractive distillation conditions including the downwardpassage of liquid solvent through line 18 into an upper portion of theextractive distillation zone 1. Heat is supplied to this column byreboiler heat input means 20 by which vapor is caused tocountercurrently contact downfalling liquid. The liquid solvent flowingdownward selectively dissolves the heaviest aromatic components of thefeed stock and the conditions in the bottom of the extractivedistillation zone are regulated so that essentially only aromaticmaterials are dissolved in the solvent. The aromatic rich solvent,

referred toas the first rich solvent stream, passes out of theextractive distillation column via line 19 to be passed into-a recoverycolumn 6. Recovery column-6 is typically a simple fractionator whichcontains reboiler means 21 which allows heat to be passed into therecovery column to cause vaporization of the heavy aromatics selectivelydissolved in the solvent passing through line 19. Regenerated leansolvent passes out of the bottom of recovery column via line 18. Aportion or all of the solvent recovered by line 18 may be passed intothe extractive distillation zone 1. It is contemplated that additionalportions of solvent from outside sources might pass into the extractivedistillation column through this line. Quantities of solvent may beremoved via line 18 for regeneration or other treating and recycled backinto the extractive distillation zone 1.

On the upper portion of recovery column 6 there is a condenser 13 whichreceives the heavy aromatic vapors through line 22, condenses them, andpasses vapors and liquid into the overhead receiver 7 which allowsliquid material to be removed from the process via line 23. A portion ofthe liquid material from the overhead receiver 7 may be refluxed vialine 24 to the recovery column to maintain top temperatures at acontrolled level.

A first overhead vapor stream which comprises essentially all of thenon-aromatics and most of the lighter aromatics present in the feedstock which originally passed via line 14 into extractive distillationcolumn 1 is withdrawn from zone 1 via line 15. The vaporous materialspassing through line 15 pass into a condenser 9 forming vapor and liquidmaterials which pass via line 15 into overhead receiver 8. Overheadreceiver 8 collects liquids and acts as a surge tank. Part of thisliquid can pass as reflux via line 17 for maintaining top temperaturecontrol in the extractive distillation zone 1. The remaining condensedfirst-overhead vapor stream passes via line 16 into the liquid phaseextractor 2. A portion of the material passing through line 16 may berecovered itself as a product, or other enriched aromatic materials maybe interjected as secondary feed stocks into line 16 to be passed intothe liquid phase ex traction zone 2.

Liquid phase extraction zone 2 is typically a vessel which can allow aliquid-liquid contacting ofliquid solvents and liquid feed stocks.Typically the liquid phase extraction zone 2 contains a rotating disccontactor or bubble-deck trays or any other internal devices which areknown in the art to promote intimate contacting of the downfallingsolvent with upflowing liquid feed stocks. Liquid feed stock passes vialine 16 preferably into a lower section of the liquid phase extractionzone 2.

The liquid phase conditions which are maintained in liquid phaseextraction zone 2 allow an essentially aromatic and solvent-freeraffinate stream, that is a stream comprising mainly non-aromatics, topass out of the liquid phase extraction zone 2 via line 26. Passing intothe uppermost portion of the liquid phase extraction zone 2'via line isa lean solvent. The solvent flows downwardly contacting liquid feedwhich passes into the extractor 2 via line 16. Also shown passing intothe extractor 2 is line 28 which carries a reflux stream which will bedefined below. The purpose of the reflux stream is to provide a lightnon-aromatic component in the lowermost portion of the extraction zonewhich can cause the heavier molecular weight non-aromatics which boilnear the boiling point of the aromatics in the solvent in this portionof the extractor to be removed from the solvent. The lighter molecularweight reflux stream is generally more soluble than the heavierparaffinic and cycloparaffinic materials.

A second rich solvent stream passes out of the liquid phase extractionzone 2 via line 27. This second rich solvent stream contains lightaromatics and some nonaromatic materials.

The stripping zone 3 functions to remove the nonaromatic materials fromthe second rich solvent stream to provide a third rich solvent streamcontaining essentially no non-aromatic materials. The stripping zone istypically a simple fractionation zone which contains a reboiler heatinput means 34 which can be regulated at a temperature which can causethe relatively highly volatile non-aromatics to be stripped from thedownfalling second rich solvent stream. The non-aromatic materialsstripped from the second rich solvent which passes into the stripper 3via line 27, pass out of the stripper via line 29 and into a condensingzone such as a heat exchanger cooler 11 to be condensed into liquids.These liquids pass via line 29 into overhead receiver 10 wherein aportion or all of the liquid passed into the receiver can be used as areflux stream which passes via line 28 into liquid phase extraction zone2. A portion of the non-aromatic reflux passing through line 28 may berecovered and additional portions, when needed, may pass into the uppersections of the stripping zone 3 to be used as a reflux stream tocontrol the top temperature in that particular zone. The stream passingvia line 29 out of the stripping zone 3 is typically referred to as asecond overhead vapor stream and contains non-aromatics and some lightaromatics.

A third rich solvent comprising the solvent and the remainingessentially non-aromatic-free aromatics passes out of the bottom portionof stripping zone 3 via line 30 and into a recovery zone 4 wherein thelight extract aromatics can be flashed or distilled overhead while therelatively aromatic-free solvent can pass as a lean solvent stream vialine 25 back into the upper portion of the liquid phase extraction zone2. A portion of a solvent returned via line 25 may be passed intoregeneration operations not shown for the removal of polymers orby-products, and additional quantities of fresh solvent can be added viathis line into this portion of the process. The light extract materialwhich comprises essentially a light aromatics fraction of the originalfeed stream passing through line 14 is recovered as a vapor via line 31and preferably is cooled via cooler 12 and passed into overhead receiver5. Line 32 can carry the light aromatic extract materials out of theoverhead receiver 5 to be collected as-product. Optionally, a portion ofthe liquid materials recovered in the overhead receiver may be passedvia line 33 back into the recovery column 4 as reflux to maintain toptemperature control in that column. Heat input means 35 can be used tocontrol the column bottoms temperature.

Not shown on the accompanying drawing are the various control meansutilized to effectively maintain levels, pressures and temperatures inthe various zones along with those means utilized to induce flow betweenthe various zones and to maintain overall stable operations. It iscontemplated that those knowledgeable in the art would be able to designspecific process control loops which can be utilized to effectivelycontrol temperatures, pressures and flow rates between and among thevarious zones and pieces of equipment described above.

DETAILED DESCRIPTION OF THE INVENTION The cost of aromatics extractionfrom a paraffin and naphthene containing feed is tied to the range ofcarbon numbers in the charge to the aromatics recovery unit by theutility requirements of operating this unit. A more economical operationoccurs with a smaller aromatic carbon number range. As an example, whenfeeding a mixture containing benzene, toluene and xylene, a moreeconomical operation of the aromatic extraction step would be achievedif the feed was split into a first fraction containing only benzene andtoluene and a second fraction containing only toluene and xylenes andthese aromatics were then extracted. The range of carbon numbers wouldin this way be reduced from 3 to 2. However, the utilities cost of thisinitial splitting of the feed has been found to offset the resultingsavings in the aromatic extraction, and the capital cost of the processis increased by the requirement of having two extraction units insteadof one.

Our invention eliminates the need for a prefractionator in a processwhich utilizes the lower utility cost of extracting aromatics fromseparate fractions having a lower carbon number range than the feedstream.

A hydrocarbon feed stock containing non-aromatic hydrocarbons andaromatic hydrocarbons including benzene and C aromatics suitable forseparation according to the process of this invention includes fluidmixtures having sufficiently high concentrations of aromatichydrocarbons to economically justify the recovery of the aromatichydrocarbons contained therein as a separate product stream. While thepresent invention is applicable to hydrocarbon feed mixtures whichcontain at least about 25 percent by weight aromatic hydrocarbons, aparticularly preferred feed mixture contains at least 75 percent byweight aromatics. A suitable carbon number range for the hydrocarbonfeed mixture is from about six carbon atoms per molecule to about carbonatoms per molecule, and more preferably from about six to about 10carbon atoms per molecule. A suitable hydrocarbon feed source is thedebutanized reactor effluent from a conventional catalytic reformingunit. Another suitable feed stock source is the liquid by-product from apyrolysis gasoline unit which has been hydrotreated to saturate olefmsand diolefms thereby producing an aromatic hydrocarbon concentratesuitable for the solvent extraction techniques hereinafter described.Typically, the feedstock derived from a catalytic reforming process orfrom pyrolysis gasoline unit will contain single ring aromatichydrocarbons comprising a wide boiling mixture of benzene, toluene andxylenes. These single ring aromatic hydrocarbons are also mixed withparaffins and naphthenes in the corresponding boiling range. Aparticularly preferred feed stock is a naphtha fraction, particularly ahydrotreated liquid by-product from a pyrolysis gasoline unit or adebutanized effluent from a catalytic reforming unit containing at leastabout 75 percent aromatic hydrocarbons by weight. Particularly preferredis a C -Qr naphtha fraction.

Solvents capable of selectively dissolving and extracting aromatichydrocarbons from a mixture of aromatic and non-aromatic hydrocarbonsare well known to those trained in the art. A preferred solvent is asolvent of the sulfolane type. A sulfolane type solvent possesses a 5member ring containing one atom of sulfur and 4 atoms of carbon with 2oxygen atoms bonded to the sulfur atom of the ring. Generically, thesulfolane type solvents have a structural formula as noted by formula 1:

wherein R., R R and R are independently selected from the groupcomprising a hydrogen atom and alkyl group having from one to 10 carbonatoms, an alkoxy radical having from one to eight carbon atoms, and anarylalkyl radical having from one to l2 carbon atoms.

Other solvents analogous to the sulfolane type so]- vents which may beincluded within this process are sulfolenes such as 2-sulfolene or3-sulfolene which have the structure as illustrated in formulas 2 and 3:

Other typical solvents which have a high selectivity for separatingaromatics from non-aromatic hydrocarbons and which may be processedwithin the scope of the present invention are Z-methylsulfolane,2,4-dimethylsulfolane, methyl 2-sulfonyl ether, naryl-3-sulfonyl amine,2-sulfonyl acetate, diethylene glycol, various polyethylene glycols,dipropylene glycol, various polypropylene glycols, dimethyl sulfoxide,N-methyl pyrollidone, etc.

A specifically preferred solvent chemical to be utilized in the presentinvention is the chemical sulfolane wherein according to formula 1, R RR and R, each comprise a hydrogen atom. The structural formula ofsulfolane is set out in formula 4:

CH: (Ba.

Since these aromatic selective solvents are well known to those trainedin the art and, in particular, since sulfolane type solvents arearticles of commerce widely utilized in the solvent extraction art,greater detail thereon need not be presented herein.

The aromatic selectivity of aromatic selective solvents such assulfolane can usually be enhanced by the addition of water to thesolvent. Preferably the solvent utilized in the practice of thisinvention contains small quantities of water to increase the selectivityof the overall solvent phase for the aromatic hydrocarbons withoutreducing in a substantial manner, the solubility of the solvent in thearomatics. Further, the presence of water in the solvent compositionprovides a relatively volatile material which can be distilled from thesolvent to vaporize the last traces of non-aromatic hydrocarbons fromthe solvent stream by steam distillation. Accordingly, a preferredsolvent composition to be utilized in the process of the presentinvention contains about 0.1 percent to about percent by weight waterand more particularly from about 0.5 to about 1 percent by weight,depending upon the particular solvent utilized and the processconditions at which the solvent extraction zone and extractivedistillation zone are operated.

The first aromatic or heavy extract stream is typically the heaviestaromatic components of the feed stock passed into the extractivedistillation zone. In particular the first aromatic fraction containsvery little, if any, non-aromatic components and in most instances willcontain less than about a few percent or even down to a few tenths of aweight percent or even less of nonaromatic components. Specifically, thefirst aromatic stream has an average boiling point which is much higherthan the average boiling point of the second or light aromatic stream.

The second aromatic or light extract streamis typically the lightestboiling aromatic components found in the feed stock passed into ourprocess. Specifically, the second aromatic stream has a lower boilingpoint and lower average molecular weight as compared to the firstaromatic stream. This stream in our process shall contain essentially nonon-aromatic components. However, in some instances the operatingconditions may be unsteady and a few weight percent of non-aromatic orreflux type material may be present in this stream.

Both first and second aromatic streams can contain water which may bepresent in the system to effect selectivity of the solvent foraromatics. Neither of these aromatic streams should contain solvent ifthe recovery systems for which they are recovered are operated properly.

The raffinate stream typically contains essentially all of thenon-aromatic components passed into our process via the feed stream tothe extractive distillation zone. The raffinate stream generallycontains small quantities of solvent which can be recovered from theraffinate by water washing it. The raffinate may also contain as many asa few percent of aromatic components due to the inability of the liquidphase extraction zone to totally recover and separate aromaticcomponents from the non-aromatic components. Typically, the raffinatestream will contain less than about 1 or 2 wt. percent of aromaticcomponents when it is recovered from a well operated process. Theraffinate stream is generally recovered from the upper portion of theliquid phase extraction zone.

The reflux stream is typically a stream comprising aromatic andnon-aromatic components which are present in the feed stock passed intoour process. Specifically the reflux stream can contain in addition tononaromatic components some of the light weight aromatic componentswhich typically are found in the second aromatic or light extract streamrecovered from the process. The reflux stream components when comparedto the raffinates non-aromatic components, are generally of loweraverage molecular weight, and have a lower average boiling point. Thereason that the reflux stream contains lighter weight non-aromaticcomponents as compared to the raffinate stream is that the lowermolecular weight non-aromatics are more easily dissolved in most polarsolvents and therefore end up in the solvent stream removed from theliquid phase extraction zone. Since the heavier weight non-aromaticcomponents may have boiling points close to the aromatics removed fromthe liquid phase solvent extraction zone, they may not be easilyseparable. The lighter non-aromatic materials which are easily separatedfrom the aromatics in solvent removed from the extraction zone can beused as reflux stream in the bottom portion of the liquid phaseextraction zone to push the heavier non-aromatic paraffin and naphthenecomponents out of the solvent phase and into the raffinate phase to beeventually recovered as raffinate material.

When the feed stock used in our process contains aromatics such asbenzene, toluene and the full range of xylene isomers along withnon-aromatic paraffins and naphthenes having carbon numbers of anywherefrom about five to about nine carbon atoms per molecule,

the first aromatic or heavy extract stream would contain essentially allof the xylene isomers, a portion of the toluene and a lesser portion ofthe benzene. The second aromatic or light extract stream would containessentially all of the benzene together with some of the toluene and alesser amount of xylene. The split in toluene between the first andsecond aromatic streams will be generally dictated by the type ofoperation taking place in the extractive distillation zone. Theraffinate recovered from such a process having the above described feedstock composition would contain essentially all of the non-aromaticparaffins and naphthenes together with a small portion of the aromaticcomponents due to the inability, in some instances, of the extractor tototally separate aromatics from nonaromatics in the liquid phaseextraction step. The reflux stream passed back into the liquid phaseextraction zone will contain appreciable quantities of aromatics alongwith lighter paraffins and naphthenes. Particularly the reflux streamcould contain such aromatics as benzene, toluene and in some rareinstances even some xylene but this is not likely.

The first overhead vapor stream removed from the extractive distillationcolumn via line 15 will contain essentially all of the non-aromaticcomponents of the feed stock which are recovered eventually as raffinatematerial. The first overhead vapor stream will also contain essentiallyall of the light aromatics which are recovered eventually from theliquid phase extraction zone. In instances in which the feed stockcomprises benzene, toluene and xylene aromatics along with C -Cparaffins and naphthenes, the first overhead vapor would containessentially all of the benzene of the feed stock together with a portionof the toluene and all of the paraffins and naphthenes.

The second overhead vapor stream comprises what is referred to in theart as a liquid phase extraction zone reflux stream. Typically, thesecond overhead vapor stream can be removed from the stripping zonewhich would receive the second rich solvent from the liquid phaseextraction zone. The second overhead vapor stream comprises portions oflight aromatic hydrocarbons which will eventually end up as the lightaromatic or extract product plus the more volatile naphthenes andparaffins present in the feed stock which is passed into the liquidphase extraction zone. Typically in an instance in which benzene,toluene, xylene aromatics and C -C paraffins and naphthenes are presentin the feed stock used in our process, the second overhead vapor streamwill contain some benzene and toluene together with more volatileparaffins and naphthenes of the raffinate stream. A typical compositionof the second overhead vapor stream or the reflux stream will be about44 mole percent aromatics and about 56 mole percent paraffins andnaphthenes. The aromatics present in the reflux are generally thelightest aromatics present in the feed stock passing into our process;the same holding true for the paraffins and naphthenes present in thisstream. The second overhead vapor stream may in some cases contain watervapor which has been stripped from the solvent in the stripping zone. Inthese instances the solvent is used with water to enhance itsselectivity.

An alternative flow that is not shown in the drawing utilizes the samecooling, condensing and collection system for the overhead vapor streamsof both the extractive distillation zone and the stripping zone on theliquid-phase extraction zone. Line 29 leaving the extractive stripperwould connect with line between the extractive distillation column andcooling means 9. This results in the reflux to the liquid-phaseextraction zone entering with the feed.

The first rich solvent stream is the solvent stream withdrawn from theextractive distillation zone and generally essentially pure aromatichydrocarbons are dissolved in it. Specifically, the aromatichydrocarbons are the heavier aromatics present in the feed stock passedinto this zone. The second rich solvent stream comprises the solventstream withdrawn from the liquid phase extraction zone and typicallycontains the lighter aromatic components of the feed stock together witha measureable portion of light and in some cases heavier paraffinic andnaphthene materials originally present in the feed stock. The third richsolvent stream withdrawn from the stripping zone is quite similar incomposition to the second rich solvent stream except that substantiallyall of the paraffins and naphthenes present in the second rich solventstream are removed from that stream with the third rich solvent streamcomprising essentially the lighter aromatic streams of the feed stock.This stream may contain small portions of paraffms and naphthenes, butin most instances will be produced as an essentially 100 percentaromatic stream on a solvent-free basis.

Extractive distillation conditions and techniques are generally wellknown to those trained in the art and vary depending upon the particularfeed stock and aromatic selective solvent utilized in the process.Typically in our invention when referring to extractive distillationconditions or an extractive distillation zone, we refer to a zone ofoperations in which a feed stock containing two fractions of aromatichydrocarbons together with non-aromatic hydrocarbons are contacted atsuch conditions, including the presence of liquid solvent selective forthe heavier aromatic hydrocarbons, as to cause essentially all of thenon-aromatic portions of the feed stock together with a sizeable portionof the aromatic fractionsand typically the light aromatic portions ofthe feed stock to be vaporized, while the liquid solvent conditions inan extractive distillation zone when utilizing a sulfolane solventinclude a pressure of anywhere from a few millimeters of mercury up toabout 50 psig. or higher, an overhead temperature varying anywhere fromF. up to 330F. or higher and a bottom temperature of about from F. up toabout 355F. or higher. Sulfolane solvent to feed ratios can varyanywhere from about 1:1 to about 20:l, depending, as do the pressure andtemperature, on feed composition. Preferred solvent to feed ratios whenprocessing a C6-C3 naphtha out are from about 2: l to about 6: 1. Theimportant factor to consider in defining extractive distillationconditions is that the feed passing into the extractive distillationcolumn is to be substantially vaporized with the heavier aromaticportion essentially solubilized in the solvent utilized.

The condensed first overhead vapor stream eventually is passed into aliquid phase solvent extraction zone maintained under aromatichydrocarbon extraction conditions including the presence of a solvent.In a preferred embodiment the solvent is of the same type utilized inthe extractive distillation zone which preferably is a sulfolanesolvent. Provided in the liquid phase extraction zone is an extractphase comprising a solvent having aromatic hydrocarbons and a minoramount of nonaromatic hydrocarbons dissolved therein and a raffinatephase comprising non-aromatic hydrocarbons. Typically, the rafflnatematerial is water washed to remove any of the solvent which may beentrained therein. Preferably, the extraction conditions utilized areregulated to maintain the solvent and hydrocarbons passed into theliquid phase extraction zone in the liquid phase to embody a liquidphase solvent extraction. As in the case of extractive distillationoperations, the conditions, apparatus and mode of operation associatedwith the solvent extraction zone are well known to those trained in theart. For example, see Petroleum Refiner, No. 8 Vol. 38, September, 1959,pages l85-l92, the teachings of which are specifically incorporated byreference into this specification.

Also embodied within the solvent extraction zone is the concept ofdisplacing non-aromatic hydrocarbons from the extract phase at the lowerend of the solvent extraction zone by utilizing the known technique of anon-aromatic reflux stream at that point. It is preferred that thisreflux stream comprise relatively light nonaromatic hydrocarbons andsome aromatic hydrocarbons. The exact reflux introduced into the lowersection of the solvent extraction zone varies depending upon the degreeof non-aromatic hydrocarbon rejection desired in the extraction zone.Preferably, the reflux is at least about l0 percent by volume of theextract phase so as to insure effective displacement of the heavynon-aromatic hydrocarbons from the extract phase into the raffinatephase. According to the process of the present invention, at least aportion, if not all, of the reflux required in a solvent extraction zoneis provided by the non-aromatic overhead stream derived from thestripping zone, preferably after condensation and water removal.

The solvent extraction zone is operated under conventional conditionsincluding elevated temperatures and a sufficiently elevated pressure tomaintain the solvent, reflux streams and hydrocarbon charge in theliquid phase. When utilizing sulfolane, suitable temperatures are about80F. to about 400F., preferably about F. to about 300F. and suitablepressures are about present in the solvent extraction zone feed.Preferred I are solvent to feed ratios, by volume, of about 2:1 to about10.1 when utilizing a C -C range naphtha cut as feed.

The extract from the liquid phase solvent extraction zone containsaromatic hydrocarbons, solvent and a lesser amount of non-aromatichydrocarbons, i.e., less than 30-50 mole on a hydrocarbon basis. It ispassed into a stripping zone to remove therefrom essentially all of thenon-aromatic hydrocarbons. The stripping zone is maintained understripping conditions well known to those trained in the art, includingmoderate pressures and sufficiently high reboiler temperatures in orderto vaporize all of the non-aromatic hydrocarbons and, as a result, aportion of the solvent and aromatic hydrocarbons from the bottomsportion of the stripping zone. This is necessary to produce a bottomsfraction stream relatively free from non-aromatic hydrocarbons andcontaining aromatic hydrocarbons and solvent. The non-aromatics areremoved overhead, in admixture with some solvent and aromatichydrocarbons, and are passed, usually after condensation and waterremoval to the hereinbefore described solvent extraction zone to provideat least a portion of specified reflux stream.

While the particular stripping zone utilized is not critical to thepractice of the present invention, the process of the present inventionis particularly suited to the utilization of the stripping zonecontained in the prior art glycol type extraction, (U.S. Pat.No.2,730,558). However, an extractive type stripper as utilized inconventional, grass roots, sulfolane units is equally suited to theprocess of the present invention. Such a stripping zone will bemaintained under a pressure of atmo spheric to about 100 psig. althougha top pressure of about psig. to about 25 psig. is preferred. Thereboiler temperature is a function of feed composition and is preferablymaintained at a level sufficient to produce a bottoms fractioncontaining less than 2000 ppm. weight non-aromatics on a hydrocarbonbasis. Maximum stripping is accomplished by introducing the extract feedinto the upper portion of the stripping zone in a manner well known tothose trained in the art.

When utilizing a stripping zone as exemplified in U.S. Pat. No.2,730,558, the liquid phase solvent extraction zone extract is firstpassed into a flash zone wherein a portion of the non-aromatics isflashed off. The remaining extract is then passed into a vaporizingsection wherein another portion of the non-aromatics are vaporized.Finally, the residue of the extract stream, now comprising sulfolanesolvent and aromatics but still containing a minor amount ofnon-aromatics, is passed to a lowermost stripping section wherein a truestripping operation of the remaining non-aromatics takes place. Thebottom of the stripping zone is typically maintained at a temperature ofabout 200F. to 500F., preferably a temperature of about 300F. to about425F. The non-aromatic hydrocarbons recovered from the various sectionsof the stripping zone are condensed and usually after intermediate waterremoval, passed as reflux to the solvent extraction zone. If desired,additional sulfolane solvent beyond that contained in the originalextract may be added to the upper portion of the stripping section toenhance aromatic recoveries therein and for improving non-aromaticrejection by improving the selectivity.

Recovering the light and heavy aromatic extract can be accomplishedthrough the use of recovery zones. Preferably, a recovering zone is afractionating zone and may typically utilize steam as an input strippingmedium to aid in the separation of the aromatic hydrocarbons from thesolvent. Typically the recovery zones are maintained under fractionationconditions generally well known to the art such as low pressures andsufficiently high temperatures to distill the respective aromatichydrocarbons overhead and to provide a relatively hydrocarbon-freeextract product stream. The recovery fractionating zone is preferablymaintained anywhere from about to about 400 millimeters pressureabsolute since subatmospheric pressures must generally be employed tomaintain a sufficiently low reboiling temperature to avoid thermaldecomposition of the sulfolane solvent.

The individual recovery or fractionating zones in which relatively puresolvent can be recovered can provide lean solvent to be used in therespective liquid phase extraction zone and the extractive distillationzone. In many instances it is preferred to operate the respectiverecovery columns independently so that the solvent utilized in theliquid phase extraction zone is maintained within a process loopincluding the liquid phase extractor, the stripping zone and recoverycolumn for those two zones. Likewise, the recovery column utilized forextractive distillation zone will allow the solvent utilized in theextractive distillation zone to be recovered in relatively pure statefrom that recovery column. It is contemplated that during normalprocessing conditions that some of the solvent from either the recoverycolumn connected to the stripping zone or the recovery column connectedto the extractive distillation zone may be diverted to the other controlloop depending upon the particular operations or factors which wouldrequire such diversion. If in a preferred instance sulfolane is used inboth the extractive distillation zone and in the liquid phase extractionzone there is no real reason why a lean solvent cannot be removed fromeither the recovery columns and passed into either the extractivedistillation column or the liquid phase extraction zone except forupsets which would be caused by varying bottoms temperatures from theseindividual recovery systems.

Each of the recovery zones may also contain full instrumentation andreflux loops to allow the overhead temperature to be maintained at agiven and controlled temperature to maintain stable operations in thezone. Likewise, both the reboiler heat input means to the individualrecovery systems may be set up upon control loops which would monitorthe bottoms temperature or any other temperature in the columns tomaintain it at a steady state to maintain stable operations throughoutthe system.

We claim as our invention:

1. A process for the recovery of two aromatic fractions andnon-aromatics from a hydrocarbon feed mixture containing aromatic andnon-aromatic hydrocarbons, which process comprises:

a. passing said feed into an extractive distillation zone maintainedunder extractive distillation conditions including the presence ofliquid solvent capable of selectively dissolving a first aromaticfraction of said two fractions to provide a first rich solvent streamcontaining said first aromatic fraction and a first overhead vaporstream comprising nonaromatic and second aromatic fraction material; b.recovering said first aromatic fraction from said first rich solvent andpassing solvent remaining after said recovery back to said extractivedistillation zone of step (a);

c. condensing at least a portion of said first overhead vapor stream toform a condensed feed;

d. passing condensed feed into a liquid phase extraction zone maintainedat extraction conditions including the presence of a liquid solventcapable of selectively dissolving the second aromatic fraction materialin said condensed feed and a hereinafter defined reflux to provide asecond rich solvent stream containing the second aromatic fraction andnon-aromatics and a raffinate phase comprising non-aromatichydrocarbons;

e. passing said second rich solvent stream into a stripping zonemaintained under stripping conditions to remove non-aromatics from saidsecond rich solvent to provide a second overhead vapor comprisingnon-aromatics and a third rich solvent stream comprising said secondaromatic fraction and solvent;

condensing second overhead vapor and returning at least a portionthereof to said liquid-liquid extraction zone of step (d) as the abovementioned g. recovering said second aromatic fraction from said thirdrich solvent and passing solvent remaining after said recovery back tosaid liquid phase extraction zone.

2. Claim 1 in that said hydrocarbon feed contains aromatics selectedfrom the group consisting of benzene, toluene, xylenes and C aromaticsand non-aromatics selected from the group consisting of paraffins andcyclo-parafflns having from about five to about nine carbon atoms permolecule.

3. Claim 2 in that said second aromatic fraction comprises benzene andtoluene.

4. Claim it in that said hydrocarbon feed contains aromatics selectedfrom the group consisting of benzene, toluene and xylenes andnon-aromatics selected from the group consisting of paraffins andcyclo-paraffins having from about five to about nine carbon atoms permolecule. t

5. Claim 4 in that said first aromatic fraction comprises toluene andxylene.

6. Claim 4 in that said second aromatic fraction comprises benzene andtoluene.

7. Claim 4 in that said raffinate stream comprises paraffins andcyclo-paraffins having from about five to about nine carbon atoms permolecule.

8. Claim 4 in that said reflux comprises paraffins and cyclo-paraffinshaving an average boiling point which is lower than the average boilingpoint of the raffinate stream.

9. Claim 1 in that at least one of said solvents comprises a sulfolanetype chemical of the general formula:

wherein R R R and R are independently selected from the group consistingof hydrogen, alkyl groups having from one to about 10 carbon atoms, andan alkoxy radical having from one to about eight carbon atoms.

10. Claim 9 in that at least one of said solvents comprises sulfolane.

ll. Claim 9 in that at least one of said solvents comprises a sulfolaneselected from the group consisting of 2-sulfolene and 3-sulfolene.

12. A process for the recovery of a heavy aromatic extract comprisingtoluene and xylene, a light aromatic extract comprising benzene andtoluene and a nonaromatic raffinate comprising paraffins andcycloparaffins having from about five to about nine carbon atoms permolecule from a hydrocarbon feed stock, which process comprises:

a. passing said feed into an extractive distillation zone maintainedunder extractive distillation conditions including the presence of asulfolane solvent to provide a first rich solvent substantially free ofnonaromatics and containing toluene and xylene and a first overheadvapor stream comprising benzene, toluene and raffinate components;

b. recovering toluene and xylene from said first rich solvent as saidheavy extract and passing solvent remaining after said recovery back tosaid extractive distillation zone of step (a);

c. cooling said first overhead vapor stream to form a condensed feed;

(1. passing condensed feed into a liquid phase extraction zonemaintained at extraction conditions including the presence of asulfolane solvent and a hereinbelow defined reflux stream to provide asecond rich solvent stream containing benzene and toluene andnon-aromatics, and a raffinate phase substantially free of aromatics;

e. passing said second rich solvent stream into a stripping zonemaintained under stripping conditions to remove non-aromatics from saidsecond rich solvent as a second overhead vapor stream containing saidnon-aromatics from said second rich solvent and from a third richsolvent substantially free of non-aromatics containing benzene andtoluene;

f. cooling second overhead vapor and returning at least a portionthereof to said liquid phase extraction zone of step (d) as said refluxstream;

g. recovering benzene and toluene from said third rich solvent as saidlight extract and passing solvent remaining after said recovery back tosaid liquidphase extraction zone of step (d).

13. Claim 12 in that said solvent utilized in said extractivedistillation and liquid-phase extraction zone is the same.

l4. Claim 13 in that said solvent comprises tetrahydrothiophenel 1-dioxide.

15. Claim 12 in that the average boiling point of said reflux is lowerthan the average boiling point of said raffinate.

l6. Claim 12 in that said first overhead vapor stream from theextractive distillation zone and said second overhead vapor stream fromsaid stripping zone are cooled and collected in a common overhead systemand said reflux of step (f) is thereby commingled with the feed to theliquid-phase extraction zone.

1. A PROCESS FOR THE RECOVERY OF TWO AROMATIC FRACTIONS ANDNON-AROMATICS FROM A HYDROCARBON FEED MIXTURE CONTAINING AROMATIC ANDNON-AROMATIC HYDROCARBONS, WHICH PROCESS COMPRISES: A. PASSING SAID FEEDINTO AN EXTRACTIVE DISTILLATION ZONE MAINTAINED UNDER EXTRACTIVEDISTILLATION CONDITIONS INCLUDING THE PRESENCE OF LIQUID SOLVENT CAPABLEOF SELECTIVELY DISSOLVING A FIRST AROMATIC FRACTION OF SAID TWOFRACTIONS TO PROVIDE A FIRST RICH SOLVENT STREAM CONTAINING SAID FIRSTPRISING NON-AROMATIC AND SECOND AROMATIC FRACTION MATERRIAL; B.RECOVERING SAID FIRST AROMATIC FRACTION SAID FIRST RICH SOLVENT ANDPASSING SOLVENT REMAINING AFTER SAID RECOVERY BACK TO SAID EXTRACTIVEDISTILLATION ZONE OF STEP (A); C. CONDENSING AT LEAST A PORTION OF SAIDFIRST OVERHEAD VAPOR STREAM TO FORM A CONDENSED FEED, D. PASSINGCONDENSED FEED INTO A LIQUID PHASE EXTRACTION ZONE MAINTAINED ATEXTRACTION CONDITIONS INCLUDING THE PRESENCE OF A LIQUID SOLVENT CAPABLEOF SELECTIVELY DISSOLVING THE SECOND AROMATIC FRACTION MATERIAL IN SAIDCONDENSED FEED AND A HEREINAFTER DEFINED REFLUX TO PROVIDE A SECOND RICHSOLVENT STREAM CONTAINING THE SECOND AROMATIC FRACTION AND NON-AROMATICHYDROCARBONS; PHASE COMPRISING NON-AROMATIC HYDROCARBONS; E. PASSINGSAID SECOND RICH SOLVENT STREAM INTO A STRIPPING ZONE MAINTAINED UNDERSTRIPPING CONDITIONS TO REMOVE NONE-AROMATICS FROM SAID SECOND RICHSOLVENT TO PROVIDE A SECOND OVERHEAD STREAM COMPRISING SAID SECONDAROMATIC THIRD RICH SOLVENT STREAM COMPRISING SAID SECOND AROMATICFRACTION AND SOLVENT; F. CONDENSING SECOND OVERHEAD VAPOR AND RETURNINGAT LEAST A PORTION THEREOF TO SAID LIQUID-LIQUID EXTRACTION ZONE OF STEP(D) AS THE ABOVE MENTIONED REFLUX; G. RECOERING SAID SECOND AROMATICFRACTION FROM SAID THIRD RICH SOLVENT AND PASSING SOLVENT REMAININGAFTER SAID RECOVERY BACK TO SAID LIQUID PAHSE EXTRACTION ZONE.
 2. Claim1 in that said hydrocarbon feed contAins aromatics selected from thegroup consisting of benzene, toluene, xylenes and C9 aromatics andnon-aromatics selected from the group consisting of paraffins andcyclo-paraffins having from about five to about nine carbon atoms permolecule.
 3. Claim 2 in that said second aromatic fraction comprisesbenzene and toluene.
 4. Claim 1 in that said hydrocarbon feed containsaromatics selected from the group consisting of benzene, toluene andxylenes and non-aromatics selected from the group consisting ofparaffins and cyclo-paraffins having from about five to about ninecarbon atoms per molecule.
 5. Claim 4 in that said first aromaticfraction comprises toluene and xylene.
 6. Claim 4 in that said secondaromatic fraction comprises benzene and toluene.
 7. Claim 4 in that saidraffinate stream comprises paraffins and cyclo-paraffins having fromabout five to about nine carbon atoms per molecule.
 8. Claim 4 in thatsaid reflux comprises paraffins and cyclo-paraffins having an averageboiling point which is lower than the average boiling point of theraffinate stream.
 9. Claim 1 in that at least one of said solventscomprises a sulfolane type chemical of the general formula:
 10. Claim 9in that at least one of said solvents comprises sulfolane.
 11. Claim 9in that at least one of said solvents comprises a sulfolane selectedfrom the group consisting of 2-sulfolene and 3-sulfolene.
 12. A processfor the recovery of a heavy aromatic extract comprising toluene andxylene, a light aromatic extract comprising benzene and toluene and anon-aromatic raffinate comprising paraffins and cyclo-paraffins havingfrom about five to about nine carbon atoms per molecule from ahydrocarbon feed stock, which process comprises: a. passing said feedinto an extractive distillation zone maintained under extractivedistillation conditions including the presence of a sulfolane solvent toprovide a first rich solvent substantially free of non-aromatics andcontaining toluene and xylene and a first overhead vapor streamcomprising benzene, toluene and raffinate components; b. recoveringtoluene and xylene from said first rich solvent as said heavy extractand passing solvent remaining after said recovery back to saidextractive distillation zone of step (a); c. cooling said first overheadvapor stream to form a condensed feed; d. passing condensed feed into aliquid phase extraction zone maintained at extraction conditionsincluding the presence of a sulfolane solvent and a hereinbelow definedreflux stream to provide a second rich solvent stream containing benzeneand toluene and non-aromatics, and a raffinate phase substantially freeof aromatics; e. passing said second rich solvent stream into astripping zone maintained under stripping conditions to removenon-aromatics from said second rich solvent as a second overhead vaporstream containing said non-aromatics from said second rich solvent andfrom a third rich solvent substantially free of non-aromatics containingbenzene and toluene; f. cooling second overhead vapor and returning atleast a portion thereof to said liquid phase extraction zone of step (d)as said reflux stream; g. recovering benzene and toluene from said thirdrich solvent as said light extract and passing solvent remaining aftersaid recovery back to said liquid-phase extraction zone of step (d). 13.Claim 12 in that said solvent utilized in said extractive distillationand liquid-phase extraction zone is the same.
 14. Claim 13 in that saidsolvent comprises tetrahydrothiophene-1,1-dioxide.
 15. Claim 12 in thatthe average boiling point of said reflux is lower than the averageboiling point of said raffinate.
 16. Claim 12 iN that said firstoverhead vapor stream from the extractive distillation zone and saidsecond overhead vapor stream from said stripping zone are cooled andcollected in a common overhead system and said reflux of step (f) isthereby commingled with the feed to the liquid-phase extraction zone.